Seismic Cable Positioning Using Coupled Inertial System Units
An apparatus and a method of its use in a marine seismic survey are disclosed. The apparatus includes a seismic survey object (106) and an inertial measurement device (130) coupled to the seismic survey object (106). The method includes taking inertial measurements of the movement of selected points on a seismic spread relative to at least one known point, and applying the inertial measurements to the known point to determine the positions of the selected points.
1. Field of the Invention
The invention pertains to seismic surveying and, more particularly, to a method and apparatus for more accurately determining the position of seismic survey objects in a marine seismic survey.
2. Description of the Related Art
Seismic exploration is conducted on both land and in water. In both environments, exploration involves surveying subterranean geological formations for hydrocarbon deposits. A survey typically involves deploying acoustic source(s) and acoustic sensors at predetermined locations. The source(s) imparts acoustic waves into the geological formations. Features of the geological formation reflect the acoustic waves to the sensors. The sensors receive the reflected waves, which are the processed to generate seismic data. Analysis of the seismic data may then indicate probable locations of the hydrocarbon deposits.
Accurate knowledge of the positions of the seismic survey objects, e.g., acoustic sources and acoustic receivers, is important to the accuracy of the analysis. In land surveys, the problem of positioning is different from in a marine situation because environmental conditions are different. Sources, sensors, and other objects, once placed, usually do not shift to any great degree. Marine surveys, however, are more dynamic, and sources, sensors and other objects move at a much higher frequency due to environmental conditions more difficult to control.
Marine surveys come in at least two types. In a first, a spread of streamers and sources is towed behind a survey vessel. Each streamer includes multiples sensors and devices, including acoustic receivers. In a second type, a spread of seismic cables, each of which includes multiple sensors, is laid on the ocean floor, or sea bottom, and a source is towed from a survey vessel. In both cases, many factors complicate determining the position of the sensors, including wind, currents, water depth, and inaccessibility.
In the second type of marine survey, where the spread of seismic cables is laid on the sea floor, much attention is paid to the positioning of the seismic cables as they are laid. One important consideration is the shape of the seismic cables as they are deployed. The shape of the seismic cable in the water during deployment, typically a catenary shape, should be known or projected if it is to be controlled effectively during deployment. Control is needed to optimize the deployment speed and accuracy. Control is also desired to avoid tangling the seismic cable with other obstructions, such as other cables or sub-sea devices. Remedial action can be taken to avoid such problems and improve the safety of sub-sea operations.
Current techniques apply various modeling techniques to project the shape and/or position of the seismic cable during deployment. These models consider the physical characteristics of the seismic cable (e.g., weight, diameter, etc.) and account for the effect of predicted sea currents on the seismic cable as it descends to the sea floor. However, such methods provide only a model, or projection, of the seismic cable's shape and are predicated on a limited knowledge of the sea's properties.
Thus, deployment, retrieval and seismic surveying using towed streamers or ocean bottom cable requires position coordinate estimates of the seismic spread, source and receivers be known with varying degrees of certainty depending on the operational and survey requirements. In order to achieve this various methods of coordinate estimation are used. There are two primary methods to estimate coordinates, either by direct measurement or by a force-resultant model computation based on force measurements. Methods using direct measurements include GPS, acoustics distances, compass directions and others are also sometimes used.
The present invention is directed to resolving, or at least reducing, one or all of the problems mentioned above.
SUMMARY OF THE INVENTIONThe present invention comprises an apparatus and a method of its use in a marine seismic survey. The apparatus comprises a seismic survey object and an inertial measurement device coupled to the seismic survey object. The method comprises taking inertial measurements of the movement of selected points on a seismic spread relative to at least one known point, and applying the inertial measurements to the known point to determine the positions of the selected points.
The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the invention is susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments herein described in detail by way of example. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTIONIllustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The survey vessel 103 or second vessel dedicated as a source vessel, also has mounted thereon an acoustic source 124 in accordance with conventional practice. In the illustrated embodiment, the acoustic source 124 is an air gun or a vibrator, but any suitable acoustic source known to the art may be used. The seismic cables 106 each include a plurality of sensor modules 127, each housing a variety of instruments including an acoustic receiver (not shown), e.g., a hydrophone or a geophone. Since the seismic cable 106 is deployed on the bottom 115, the acoustic receivers in the illustrated embodiment are geophones. The seismic cables 106 also include, in accordance with the present invention, a plurality of inertial positioning devices (“IPDs”) 130, described more fully below, including at least one inertial measurement unit (“IMU”, not shown in
In the illustrated embodiment, the body of water 112 is an ocean, and the bottom 115 may therefore be referred to as a “seabed” or an “ocean bottom.” Accordingly, the seismic cable 106 may be referred to as an “ocean bottom cable” (“OBC”). However, the invention is not so limited. The body of water 112 may be any body of water, whether saltwater, freshwater, or brackish water. The invention may therefore be employed in marine environments, lakes, and other bodies of freshwater, or in transitional zones including brackish water. Similarly, the invention may be deployed on seismic streamers, as will be discussed further below. Note that the term “marine” is used in accordance with industry usage, and describes a survey conducted in any aquatic environment regardless of whether the water is salt, fresh, or brackish.
The invention is also not limited to marine surveys employing OBCs 106. Consider, for instance, the seismic survey 200, illustrated in
Returning to
The IPDs 130 do not steer the seismic cable 106 during deployment in the embodiment of
Turning now to
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- Arvid Hedvalls backe 4
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This micro-INS can navigate in conditions as difficult as 50 g accelerations and rotation speeds up to 3000 deg/s, combined with a bandwidth of at least 0-200 Hz. All degrees of freedom are computed and available to the user, such as yaw, pitch and roll angles, and position. Currently, the micro-INS is constructed in a 50 mm cube, and efforts are being made to reduce this size further. However, other small IMUs may be used in alternative embodiments. In one embodiment, the inertial measurement devices may be sampled at 1000 Hz using 24-bit analog-to-digital (“A/D”) converters. The control system converts sensor data into a coordinate system that can be used by other systems.
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The IPDs 130 of the illustrated embodiment are operated as an autonomous system, independent of the seismic cable electronics system, with its own power supply and communication system. When the main seismic cable power is up, the IPDs 130 are powered from the survey vessel 103, and communicate by primary communications. When the main power is down, the IPDs 130 are powered from the “bird” battery and communicate using secondary communications. As noted earlier, alternative embodiments may implement these functionalities differently.
In accordance with the present invention, the seismic cable 106 is deployed into the water 112 at a known point, e.g., the point 400. The known point 400 is a fixed reference point on the back deck of the deployment vessel 103 where the IPD/IMU coordinates are initiated. Note that the point 400 is “known” in the sense that its position can be estimated with relatively high accuracy, e.g., much better accuracy than is needed for the estimation of the position of the sensor modules. The position of the point 400 can be known, for example, from Global Positioning System (“GPS”) measurements from a GPS receiver with antenna (not shown) aboard the survey vessel 103. A GPS receiver may be placed on the equipment used to deploy the seismic cable 106 into the water 112, for instance, just before the IPD 130 leaves the deployment device. As the seismic cable 106 descends to the bottom 115, the aforementioned environmental conditions cause the seismic cable 106 to deviate in all three directions. The IMUs 300, shown in
The survey vessel 103 houses a data collection system (not shown) that may also, in some embodiments, be used to determine the positions of the IPDs 130, 230.
The processor 505 runs under the control of the operating system 530, which may be practically any operating system known to the art. The application 565 is invoked by the operating system 530 upon power up, reset, or both, depending on the implementation of the operating system 530. The computing apparatus 500 may be, for instance, a rack-mounted personal computer. Similarly, the computing apparatus 500 may be implemented as a workstation. However, this is not necessary to the practice of the invention, and any suitable computing apparatus may be employed.
Note that the physical location at which the processing occurs is not material to the practice of the invention. The data may be processed at the point of collection, e.g., aboard the survey vessel 103 in
A computing apparatus, such as the one illustrated in
For instance, in the embodiment of
Returning now to
In some embodiments, such as the seismic survey 200 in
However, as will be appreciated by those skilled in the art, environmental conditions, such as currents and winds, will frequently re-position the streamers 206 of the seismic spread 202. In conventional practice, a seismic spread 200 will include one or more birds and/or steering devices to steer the streamers and maintain their desired position. The IPDs 230 are, also as mentioned above, modified birds or steering devices that can still be used for steering the streamers 206. During deployment of the survey equipment, subsequently during the conduct of the survey, and post survey during the retrieval of the equipment, the inertial measurement units 300 of the IPDs 230 may take inertial measurements of their deviation and transmit them to the data collection unit aboard the survey vessel 103. The data collection system can analyze the inertial measurements and then issue appropriate steering commands to the IPDs 230 to maintain the respective streamer 206 in its desired position, which can vary depending on the immediate objective, e.g., to improve the survey or address a safety concern. Note that this is but one example in which the present invention may be employed post-deployment and during the conduct of the seismic survey 200. Other uses will become apparent to those skilled in the art having the benefit of this disclosure.
It may sometimes be desirable to obtain an additional degree of accuracy in the positions of sensor modules 127. After the IPD/IMU leaves the back deck of the deployment vessel 103, the coordinate estimates are in reference to the initial coordinates and the measurements of change relative to this point start to degrade with time until they are refreshed with a coordinate estimate update from the navigation system. The measurements of the IPDs 130, 230 can be supplemented by other measurements, for instance, by tightly integrating one-dimensional measures such as acoustic ranges, range differences and pressure differences.
For example, returning to
In the embodiment of
The acoustic sources 406 generate acoustic ranging signals 403 (only three indicated) that are received by the acoustic receivers of the sensor modules 227. The acoustic receivers receive the acoustic ranging signals 403 and transmit them to the data collection system aboard the survey vessel 103, which then applies them to the inertial measurements to calibrate the measured position of the IPDs 130.
Calibration of the inertial unit can be accomplished by a variety of methods and is analogous to calibration of a strapdown IMU in an Inertial Navigation System. Kalman filter INS calibration is a well known method of estimating INS errors. One common Kalman filter often used is an open-loop system 900, illustrated in
Note that the spatial resolution of the positioning information obtained by application of the present invention will be largely determined by the number of IPDs 130, 230 that are employed. In theory, any number of IPDs 130, 230 may be employed. As a practical matter, the lower bound for any given implementation will be governed by some desired, minimal level of resolution. The upper bound will be determined by practical considerations such as weight, power consumption, bandwidth consumption, and cost. However, the number of IPDs in any given embodiment is not material to the practice of the invention. Note also that the invention is not limited to the positioning of seismic cables. The present invention may be applied to determine the position of any seismic survey object. A seismic survey object can be any object that may be employed in the conduct of a seismic survey, excluding vehicles. Thus, survey vessels, autonomous unmanned vehicles, (“UAVs”), remotely operated vehicles (“ROVs”), and the like are excluded while other pieces such as seismic cables, and acoustic sources (e.g., the acoustic sources 124 in
The definition seismic survey object also includes autonomous objects that are not vehicles. For instance, some embodiment may employ acoustic sources or sensor modules that are “autonomous” in the sense that they are not linked by seismic cables. Such a survey 800 is shown in
The present invention therefore comprises an apparatus and a method of its use in a marine seismic survey. The apparatus comprises a seismic survey object and an inertial measurement device coupled to the seismic survey object. The seismic survey object may be, for instance, a seismic cable (e.g., the OBC 106 or streamer 206 in
The method comprises taking inertial measurements of the movement of selected points (i.e., locations of the RMs 300) within a seismic spread relative to at least one known point (e.g., the point of deployment 400), and applying the inertial measurements to the known point to determine the positions of the selected points. The inertial measurements can be taken either during deployment, as shown in
Thus, in its various aspects and embodiments, the present invention may provide, relative to the state of the art, one or more advantages including:
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- an additional observation type to calibrate non inertial observations that can increase reliability in the overall system;
- continuity of positioning during periods of lost or distorted complimentary measures, such as acoustic distances or GPS control; and
- depending on inertial sensor drift rates, a reduction in the frequency and number of acoustic measurements used to recalibrate the inertial system (i.e., with no drift rate, or an insignificant drift rate over the course of a deployment, and a high enough spatial frequency of inertial units, positioning could be determined without acoustics).
Additional advantages and benefits may become apparent to those skilled in the art having the benefit of this disclosure.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.
Claims
1. An apparatus for use in a marine seismic survey, comprising:
- a seismic survey object; and
- an inertial measurement unit coupled to the seismic survey object.
2. The apparatus of claim 1, wherein the seismic survey object comprises one of a seismic cable, a seismic receiver, a steering device, and a seismic source.
3. The apparatus of claim 2, wherein the seismic cable comprises one of a streamer and an ocean bottom cable.
4. The apparatus of claim 2, wherein the seismic cable includes one of a sensor module, a steering device, and an inertial positioning device in which the inertial measurement unit is housed.
5. The apparatus of claim 2, wherein the seismic cable includes a plurality of acoustic receivers.
6. The apparatus of claim 2, wherein the steering device comprises one of a Q-fin and a bird.
7. The apparatus of claim 2, wherein the seismic source comprises at least one of an air gun and a vibrator.
8. The apparatus of claim 1, further comprising an inertial positioning device in which the inertial measurement unit is housed.
9. The apparatus of claim 1, wherein the inertial positioning device further comprises:
- a power system for the inertial measurement unit;
- a communication interface; and
- a battery powering the power system and the communication interface.
10. The apparatus of claim 1, wherein the inertial measurement unit comprises a plurality of accelerometers and gyroscopes.
11. The apparatus of claim 1, wherein the inertial measurement unit comprises a micro-electromechanical inertial measurement unit.
12. The apparatus of claim 8, wherein the inertial positioning device further comprises an acoustic node determined by either an acoustic source or receiver.
13. The apparatus of claim 12, wherein the acoustically determined point comprises one of an ultra-short baseline acoustic system, a short baseline acoustic system, or a distance measurement acoustic system.
14. A marine seismic spread, comprising:
- a plurality of seismic survey objects, including a plurality of acoustic receivers and at least one acoustic source, distributed over a survey area from at least one known point; and
- a plurality of inertial positioning devices coupled to the seismic survey objects and capable of taking inertial measurements of the movement of the seismic survey objects relative to the known point.
15. The marine seismic spread of claim 14, wherein the plurality of seismic survey objects include a plurality of seismic cables comprised of the acoustic sources and the inertial positioning devices.
16. The marine seismic spread of claim 15, wherein the seismic cables comprise one of a plurality of streamers and a plurality of ocean bottom cables.
17. The marine seismic spread of claim 14, wherein the seismic survey objects include a one of a plurality of a plurality of inertial positioning devices and a plurality of steering devices in which the inertial positioning devices are housed.
18. The marine seismic spread of claim 14, wherein the plurality of acoustic receivers comprise a plurality of hydrophones or geophones.
19. The marine seismic spread of claim 14, wherein the inertial measurement unit is housed in an inertial positioning device.
20. The marine seismic spread of claim 18, in which the inertial positioning device further comprises:
- a power system for the inertial measurement units;
- a communication interface; and
- a battery powering the power system and the communication interface.
21. The marine seismic spread of claim 14, wherein at least one of the inertial measurement units comprises a plurality of accelerometers and gyroscopes.
22. The marine seismic spread of claim 14, wherein at least one of the inertial measurement units comprises a micro-electromechanical inertial measurement unit.
23. The marine seismic spread of claim 19, wherein the inertial positioning device further comprises an acoustic node determined by either an acoustic source or receiver.
24. The marine seismic spread of claim 23, wherein the acoustic source comprises one of an ultra-short baseline acoustic system, a short baseline acoustic system, or a distance measurement acoustic system.
25. An apparatus for use in a marine seismic survey, comprising:
- a seismic cable; and
- an inertial measurement unit coupled to the seismic cable.
26. The apparatus of claim 25, wherein the seismic cable comprises one of a streamer and an ocean bottom cable.
27. The apparatus of claim 25, wherein the seismic cable includes one of a sensor module, a steering device, and an inertial positioning device in which the inertial measurement unit is housed.
28. The apparatus of claim 25, wherein the seismic cable includes a plurality of acoustic receivers.
29. The apparatus of claim 28, wherein the plurality of acoustic receivers comprise a plurality of hydrophones or a plurality of geophones.
30. The apparatus of claim 25, wherein the inertial measurement unit is housed within an inertial positioning device.
31. The apparatus of claim 30, wherein the inertial positioning device further comprises:
- a power system for the inertial measurement units;
- a communication interface; and
- a battery powering the power system and the communication interface.
32. The apparatus of claim 25, wherein at least one of the inertial measurement units comprises a plurality of accelerometers and gyroscopes.
33. The apparatus of claim 25, wherein at least one of the inertial measurement units comprises a micro-electromechanical inertial measurement unit.
34. The apparatus of claim 30, wherein the inertial positioning device further comprises an acoustic node determined by either an acoustic source or receiver.
35. The apparatus of claim 34, wherein the acoustic source comprises one of an ultra-short baseline acoustic system, a short baseline acoustic system, or a distance measurement acoustic system.
36. A method for use in a marine seismic survey, comprising:
- taking inertial measurements of movement of selected points on a seismic spread relative to at least one known point; and
- applying the inertial measurements to the known point to determine the positions of the selected points.
37. The method of claim 36, wherein taking the inertial measurements includes taking the inertial measurements during at least one of deploying the spread, retrieving the spread and conducting a survey.
38. The method of claim 36, further comprising supplementing the inertial measurements.
39. The method of claim 38, wherein supplementing the inertial measurements comprises at least one of calibrating the positions using a coordinate history determined from acoustic ranging signals and integrating one dimensional measures such as acoustic ranges, range differences and pressure differences.
40. The method of claim 36, further comprising deploying the seismic spread at the known point.
41. The method of claim 40, wherein deploying the seismic spread at the known point includes one of deploying the seismic spread to the bottom of a body of water and deploying the seismic spread near to the surface of the body of water.
42. The method of claim 40, wherein deploying the seismic spread at the known point includes deploying the seismic spread in one of saltwater, fresh water, and brackish water.
43. The method of claim 36, further comprising housing an inertial measurement unit in a seismic survey object.
44. The method of claim 43, wherein housing the inertial measurement unit in a seismic survey object includes housing the inertial measurement unit in one of a seismic cable, a seismic receiver, a steering device, and a seismic source.
45. The method of claim 36, wherein taking inertial measurements of the movement of selected points on the seismic spread includes taking inertial measurements of the movement of selected seismic survey objects.
46. The method of claim 45, wherein taking inertial measurements of the movement of selected seismic survey objects includes taking inertial measurements of the movement of at least one of a seismic cable, a seismic receiver, a steering device, and a seismic source.
47. The method of claim 36, wherein the seismic cable includes seismic survey objects having known relative orientations with respect to the selected points on the seismic cable, and the method further comprises determining positions of the selected seismic survey objects based on the determined positions of the selected points and the known relative orientations.
48. A method for use in a marine seismic survey, comprising:
- deploying a seismic cable at a known point;
- taking inertial measurements of movement of selected points on the seismic cable relative to the known point during the deployment; and
- applying the inertial measurements to the known point to determine the positions of the selected points.
49. The method of claim 48, wherein the seismic cable includes seismic survey objects having known relative orientations with respect to the selected points on the seismic cable, and the method further comprises determining positions of the selected seismic survey objects based on the determined positions of the selected points and the known relative orientations.
50. The method of claim 48, wherein deploying the seismic cable comprises one of deploying the seismic cable to the bottom of the water and deploying the seismic cable near to the surface of the water.
51. The method of claim 48, further comprising supplementing the inertial measurements.
52. The method of claim 51, wherein supplementing the inertial measurements comprises at least one of calibrating the positions using a coordinate history determined from acoustic ranging signals and integrating one dimensional measures such as acoustic ranges, range differences and pressure differences.
53. The method of claim 51, wherein deploying the seismic cable at the known point includes one of deploying the seismic cable to the bottom of a body of water and deploying the seismic cable near to the surface of the body of water.
54. The method of claim 51, wherein deploying the seismic cable at the known point includes deploying the seismic cable in one of saltwater, fresh water, and brackish water.
55. The method of claim 48, further comprising housing an inertial measurement unit in a seismic survey object comprising a portion of the seismic cable.
56. The method of claim 55, wherein housing the inertial measurement unit in a seismic survey object includes housing the inertial measurement unit in one of a seismic receiver, a steering device, and a seismic source.
57. The method of claim 48, wherein taking inertial measurements of the movement of selected points on the seismic cable includes taking inertial measurements of the movement of selected seismic survey objects comprising a portion of the seismic cable.
58. The method of claim 57, wherein taking inertial measurements of the movement of selected seismic survey objects includes taking inertial measurements of the movement of at least one of a seismic receiver, a steering device, and a seismic source.
59. A method for use in a marine seismic survey, comprising:
- conducting a survey with a seismic spread deployed from at least one known point;
- taking inertial measurements of movement of selected points on the seismic spread relative to the known point during the conduct of the seismic survey; and
- applying the inertial measurements to the known point to determine the positions of the selected points.
60. The method of claim 59, further comprising supplementing the inertial measurements.
61. The method of claim 60, wherein supplementing the inertial measurements comprises at least one of calibrating the positions using a coordinate history determined from acoustic ranging signals and integrating one dimensional measures such as acoustic ranges, range differences and pressure differences.
62. The method of claim 59, further comprising deploying the seismic spread at the known point.
63. The method of claim 62, wherein deploying the seismic spread at the known point includes one of deploying the seismic spread to the bottom of a body of water and deploying the seismic spread to the surface of the body of water.
64. The method of claim 62, wherein deploying the seismic spread at the know point includes deploying the seismic spread in one of saltwater, fresh water, and brackish water.
65. The method of claim 59, further comprising housing an inertial measurement unit in a seismic survey object.
66. The method of claim 65, wherein housing the inertial measurement unit in a seismic survey object includes housing the inertial measurement unit in one of a seismic cable, a seismic receiver, a steering device, and a seismic source.
67. The method of claim 59, wherein taking inertial measurements of the movement of selected points on the seismic spread includes taking inertial measurements of the movement of selected seismic survey objects.
68. The method of claim 67, wherein taking inertial measurements of the movement of selected seismic survey objects includes taking inertial measurements of the movement of at least one of a seismic cable, a seismic receiver, a steering device, and a seismic source.
69. The method of claim 59, wherein the seismic cable includes seismic survey objects having known relative orientations with respect to the selected points on the seismic cable, and the method further comprises determining positions of the selected seismic survey objects based on the determined positions of the selected points and the known relative orientations.
Type: Application
Filed: Jan 29, 2004
Publication Date: Oct 16, 2008
Inventors: Kenneth E. Welker (Nesoya), Vidar A. Husom (Asker)
Application Number: 10/597,227
International Classification: G01V 1/38 (20060101);